The present invention relates to an apparatus for grinding at least the periphery of spectacle lenses. The apparatus comprises at least one grinding wheel, at least one rotatable holder for a lens blank, and at least one device for CNC (computerized numerical control) controlled grinding of the blank according to selected optical specifications and/or a selected contour of the lens to be produced.
Such a device is known from German Offenlegungsschrift 41 27 094. The disclosed apparatus comprises at least one input device connected to the control device for inputing optical specifications of the lens to be produced and/or for the decentralization values of the predetermined contour and/or the position of the optical axis and/or the position of the reading portion of the lens with respect to the optical axis as well as at least one manipulation device connected to the control unit for taking up and positioning the lens blank according to the specifications and values input with the inputting device and for a corresponding precise positioning of the lens blank on the holder. The manipulation device picks up one of the lens blanks at the edge and guides it into the open holder of the grinding machine. The manipulation device is controlled such that the lens blank with respect to the rotational axis of the holder is positioned corresponding to the input decentralization data. When the holder subsequently clamps the lens blank and the manipulation device releases the lens blank, the grinding process can be preformed according to the selected optical specifications and/or according to the selected contour of the lens to be produced while taking into consideration the decentralization values. When the holder is designed such that it can clamp the lens blank so as to be rotationally fixed, after having been exactly positioned by the manipulation device, it is no longer necessary to provide for a blocking of the lens blank before insertion into the holder of the grinding machine. In addition to or instead of the decentralization values it is also possible to take into consideration via the input device the axial position of the selected contour of a lens to be produced with cylindrical or prismatic grinding and/or the optical specifications of the lens to be ground, i.e., for bifocal or trifocal lenses the position of the reading portion.
In order to be able to automatically align the lens blank the known apparatus may be provided with a vertex refractometer positioned within the operating range of the manipulation device. This vertex refractometer comprises a sensor and a data connection to the control device and is used for positioning at the optical center point the lens blank held by the manipulation device and for registering the data of the optical center point for the subsequent position-exact insertion of the lens blank on the holder.
The known apparatus furthermore provides the possibility of controlling the manipulation device with machine-readable markings of the optical values provided at the lens blank. The lens blank which has been taken up by the manipulation device can be guided into the area of a sensor which then reads the optical specifications. With a data connection to the control device the position-exact insertion of the lens blank into the holder can be preformed as a function of the optical specifications that have been detected by the sensor and also as a function of the preset decentralization values and/or the optical axis position.
Furthermore, it should be mentioned that a large number of different lens blanks can be arranged within a container that is accessible to the manipulation device whereby for each of the lens blanks a machine-readable marking as an address is provided at the container which address is read by the sensor provided at the manipulation device and controls via the data connection to the control device, the removal of a lens blank from the container according to the selected optical specifications.
It is therefore an object of the present invention to provide an apparatus for grinding at least the periphery of lens blanks comprising a detection system for markings at the lens blanks which is responsive to conventional markings such as points, crosses, notches at the edge of the lens blank, or the position of a reading portion of the lens that is already ground into the lens blank.